When installing a directional antenna, it is important to orient it toward an appropriate direction in order to maximize the reception level. Since radio waves at millimeter-wave frequencies have been used recently, it is required to set the antenna orientation with respect to the wave source antenna with a level of accuracy equivalent to the accuracy needed to thread the eye of a needle. For example, extremely fine angle adjustment of 1.0° or less, such as 0.4° or 0.2°, is required today. Various methods for setting the antenna orientation (i.e., orientating the antenna) toward the wave source direction have been proposed (for example, Patent Literature 1, 2 and 3).